I. Field of the Invention:
This invention relates generally to electrosurgical apparatus and more particularly to an electrosurgical instrument for facilitating the severing of the internal mammary artery for use in coronary bypass surgery.
II. Discussion of the Prior Art:
In performing one form of a coronary bypass surgical procedure, a segment of a blood vessel harvested from another portion of the body is used as an autogenous graft to effectively bypass a stenosed segment of a coronary artery to restore adequate blood flow distal of the blockage. In such procedure, a segment of the saphenous vein is stripped from the patient's leg and subsequently used as the bypass graft. In a significant number of cases, the resulting wound to the leg is slow to heal and a cause of considerable pain and irritation.
Rather than harvest the saphenous vein, surgeons have also utilized the internal mammary artery which depends from the long thoracic artery behind the first and second rib. During open heart surgery, a thoracotomy is performed and the chest wall is retracted to provide access. The internal mammary artery is tucked beneath the upper rib cage and in order to sever the internal mammary artery from surrounding tissue, the surgeon must insert a scalpel at a particular angle to gain purchase to that artery. Once freed of surrounding tissue, the artery is cut and the free end is subsequently anastomosed to the coronary blood supply to the heart muscle. Moreover, because the internal mammary artery has a number of branches which must be cut and stapled, the procedure tends to result in a significant blood loss and, accordingly, prompt hemostasis is required.
The present invention comprises an electrosurgical instrument specifically designed for facilitating the severing of the internal mammary artery wile maintaining its condition to allow its severed end to be anastomosed to the diseased coronary artery distal of its stenosis. It comprises a pen-like handle having a proximal end and a distal end. Mounted on this handle are one or more control switches for controlling the application of RF energy to a blade member. The handle is arranged to be coupled through a cord or cable to an electrosurgical generator. Mounted in the distal end portion of the handle member is a bendable tubular segment which preferably is formed from a suitable metal that can be bent or shaped during use to a desired angular orientation without kinking. Mounted on the end of the bendable segment is a blade holder in the form of a molded plastic body having a cavity therein for containing a piezoelectric crystal and a socket for receiving the end of the blade member.
The blade member itself comprises an elongated thin insulating substrate, preferably a high temperature ceramic, which is beveled along its opposed edge and end surfaces. Electrodes in the form of metallic traces are then disposed on the substrate proximate the beveled edges so as to create a gap across the edge from a conductive trace on one major surface to an electrode on the opposite major surface. The blade may further include further electrodes centrally disposed on the substrate and spaced from the edge electrodes by a predetermined gap.
When the blade member is inserted in the socket in the blade holding member, a portion of the blade is in contact with the transducer and the transducer terminals as well as the electrode traces are coupled by conductors back through the bendable tube and through the hand to the cable.
In use, the surgeon may appropriately bend the tubular member on the end of the handle to an appropriate angle whereby the blade may be inserted beneath the retracted and raised chest wall and brought into engagement with the internal mammary artery. By depressing a first control switch on the handle, an RF voltage is applied not only across the cut electrodes, but also across the transducer's contacts so as to impart high frequency vibration of a very small stroke to the blade as it cuts through the tissue comprising the internal mammary artery. The flow of blood may be stemmed through coagulation by depressing a second handle control switch whereby the RF energy is applied between a cut electrode and a larger area coag electrode. Again, operation of the coag switch also results in energization of the piezoelectric crystal comprising the ultrasonic transducer. As is explained in the Stasz U.S. Pat. No. 4,674,498, the vibration of the blade during cutting and coagulation functions to maintain it relatively more free of charred tissue which might otherwise render the electrosurgical instrument less effective.